1. 5.3 Periodic Trends Students will understand the Shielding Effect.
Students will explain the Atomic Radius Trend found on the Periodic Table.

2. What are Periodic Trends?
Trends are properties that increase or decrease in a period or group for a specific property.
No transition metals, too many exceptions.
They are not perfect, but they are useful.

3. We will examine three trends (patterns) found on the Periodic Table. 1
We will examine three trends (patterns) found on the Periodic Table Atomic Radius 2. Ionization Energy 3. Electronegativity

4. Trend #1 Atomic Radius
Half the distance between two nuclei of the same atom (basically the size of the atom). Measured in pm

5. How Does it Work?
As you move down a group- electrons are placed on higher energy levels- so there is less pull on them form the protons in the nucleus. The atoms are larger As you move across a period from right to left –there are fewer electrons shoved into the same energy level , so less of a pull from the protons. The atoms are larger.

6. ATOMIC RADIUS
INCREASE
INCREASES

7. What does it look like? Examples:
Put in increasing order (smallest to largest):
K, Kr, Ge
Cs,, Na, K
What does it look like?

8. CHECKPOINT #1
Which of these alkali metals has the largest atomic radius? Cs, Fr, Li, or Na?

9. CHECKPOINT #2- Pg. 151
Rank the following elements by increasing (smallest to largest)atomic radius: C, Al, O, K

10. CHECKPOINT #3
Periodic trends vary as we move across the periodic table. In general, as you move across a row in the periodic table
A) ionic size increases
B) atomic radius decreases
C) nuclear charge decreases
D) ionization energy decreases

11. The Trends are explained by the Shielding Effect?
The attraction of the valence electrons to the protons in the nucleus. The further away they are from the protons, the less the attraction.

12. How Does it Work?
As you down a group, (further from the pull of the protons in the nucleus), there is more shielding on the electrons, so the atomic radii increases.
As you move across the periods from right to left, the number of protons decreases, exerting less “pull” on the electrons; therefore making the atomic radii increase.

13. Trend #2 Ionization Energy
The amount of energy required to remove an electron from an atom.
More shielding = less ionization energy
Less Shielding = more ionization energy (electrons held tight)

14. How Does it Work?
* As you move up a group, (closer to the nucleus), there is less shielding on the electrons, so more energy is required to remove then. Ionization Energy Increases.
As you move across the periods from left to right, the number of protons increase, exerting more “pull” on the electrons; therefore making them harder to remove. Ionization Energy Increases.

15. IONIZATION ENERGY
INCREASES
INCREASES

16. What Does it Look Like? Pg.153
Examples:
Put in increasing order (smallest to largest):
K, Kr, Ge
Cs, Na, K

17. Trend #3 Electronegativity
The ability of an atom’s nucleus to attract electrons from a different atom within a covalent bond.
A higher electronegativity value correlates to a stronger pull on the electrons in a bond.
Noble gases left out of this trend, they don’t attract any electrons.
More shielding= Less electronegativity
Less Shielding = more electronegativity

18. How Does it Work?
* As you move up a group, (closer to the nucleus), there is less shielding on the electrons, so those electrons are harder to attract. Electronegativity Increases.
As you move across the periods from left to right, the number of protons increase, exerting more “pull” on the electrons; therefore making them harder to attract. Electronegativity Increases.

19. ELECTRONEGATIVITY
INCREASES
INCREASES

20. What Does it Look Like? Pg. 161
Examples:
Put in increasing order (smallest to largest):
K, Kr, Ge
Cs, Na, K

21. PRACTICE #2
Rank the following elements by increasing electronegativity (lowest to highest ) : S, O, Ne, and Al

22. Classwork / Homework
Periodic Trend Worksheet